The feasibility and significance of preservation of the lobular branch of the great auricular nerve in parotidectomy

Abstract

This study was designed to evaluate the feasibility and significance of preserving the lobular branch of the great auricular nerve (GAN) during parotidectomy. Ninety-three patients with benign tumour undergoing parotidectomy were separated randomly into three groups. Thirty-one patients underwent a parotidectomy with the main trunk of GAN sacrificed (group A), 29 patients had the posterior-auricular branch preserved (group B), and 33 patients had the lobular branch preserved (group C). The operating times were recorded. Tactile sensitivity and pain sensitivity were evaluated preoperatively and at 1 week, 1 month, 3 months, 6 months and 1 year after surgery. Eighty-three patients were followed-up. Preservation of the lobular branch required no extra operating time. In group C, sensitivity in the lobular region reached preoperative levels by 6 months after surgery. In the other groups, recovery of sensory function in the lobular region was partial. Patients with the lobular branch of GAN preserved had significantly better sensory recovery in the lobular region 1 year after surgery ( P < 0.05). These results demonstrate that preservation of the lobular branch of GAN is technically feasible during parotidectomy. The preservation of the lobular branch of GAN guarantees improvement of postoperative sensitivity of the lobular region.

Parotidectomy is a relatively common surgical procedure for the treatment of parotid neoplasms and is occasionally performed for inflammatory and autoimmune conditions. During parotidectomy, the great auricular nerve (GAN) is frequently sacrificed to expedite mobilization of the inferior pole. Studies have shown that loss of GAN sensory function can lead to numbness, increased risk of injury, discomfort when wearing earrings or shaving and suffering a burn .

The idea of GAN preservation is not recent; it was first proposed by B rown et al. in 1989 . The value of GAN preservation became controversial when P orter et al. asserted that it was unnecessary, as they failed to show any advantages in the recovery of sensation when adding such a procedure .

In previous studies , most authors compared sensory recovery within the GAN sacrifice group and the GAN preservation group. In the latter group, parotidectomy was performed with the posterior branch of GAN preserved. Recent studies have shown that distinct difference between the two groups existed mostly in the lobule . Anatomically, the lobular region is innervated by the lobular branch of GAN but not the posterior branch. To improve recovery of sensation in the lobular region, it is necessary to clarify which branch of GAN should be preserved. The authors’ clinical practice has shown that preservation of the lobular branch alone can lead to an optimistic outcome. They hypothesize that the preservation of the lobular branch, not the posterior branch, is of clinical significance during parotidectomy.

In the present study, 93 patients were separated into three groups, with lobular branch preservation in one group. The purpose of this study is to assess the postoperative effects of preserving the posterior branch and the lobular branch of GAN.

Two different sensory parameters are used: tactile sensitivity (A-β fibre) and pain sensitivity (A-δ and C fibre). Other parameters, such as two-point discrimination, are not assessed. It has been reported that two-point discrimination might not depend only on the quantity but also the density of the receptors and afferent fibres. The evaluation of two-point discrimination has also been reported to result in discrepancy that may not reflect GAN recovery . Patients had a preoperative two-point discrimination of 2 cm or more, and a 4 cm evaluation was not possible because it would have gone beyond the limits of the researched regions . Thermal sensitivity is another important parameter, but it reflects the function of A-δ and C fibres as well as pain sensitivity; and the evaluation of thermal sensitivity had been proved unconvincing . For these reasons, thermal sensitivity was not chosen as the sensory parameter in this study.

Materials and methods

From January 2005 to November 2007, 93 patients underwent parotidectomy, these included patients with a preoperative diagnosis of benign parotid gland disorders. Those who had malignant tumours, recurrence or mental disability were excluded. Patients with any branch of GAN infiltrated by tumours were also excluded. Informed consent was obtained from all the enrolled patients.

All the patients were separated randomly into three groups. In group A, 31 patients underwent parotidectomy with sacrifice of the main trunk of GAN. In group B, 29 patients underwent parotidectomy with sacrifice of the lobular branch and preservation of the posterior-auricular branch. In group C, 33 patients underwent parotidectomy with sacrifice of the posterior-auricular branch and preservation of the lobular branch.

The operations were conducted with traditional ‘s-shaped’ incisions. In the process of raising the superficial subcutaneous layer, efforts were made to preserve the main trunk of GAN, which winds around the back of the sternocleidomastoid muscle and ascends the muscle to divide into branches. When GAN reaches a level 0–2 cm above the mandibular angle, it trifurcates into the anterior (auricular) branch, the posterior (auricular) branch, and the lobular branch. The anatomic structure of the bifurcation of GAN was recorded. In group B and C, the preserved branch was retracted backwards and isolated before proceeding with the operation. When the fascia connecting the parotid gland to the sternocleidomastoid muscle was cut, the branches could be preserved by careful dissection.

The methods of evaluation of tactile sensitivity and pain sensitivity were modified from V ieira et al. Tactile sensitivity and pain sensitivity were evaluated in the superior helix, pre-auricular region, posterior-auricular region, lobular region and infra-auricular region, preoperatively and at 1 week, 1 month, 3 months, 6 months and 1 year after surgery. The superior helix was defined as the superior one-third of the auricle. The posterior-auricular region was defined as an area between the posterior auricle insertion and the hairline. The infra-auricular region was defined as the location between the auricle and the angle of the mandible. The lobular region was defined as the inferior part of the auricle. For the pre-auricular region, the superior, anterior and inferior borders are the zygoma, the anterior border of masseter muscle, and the level of the inferior border of the lobule, respectively.

The examiner and patients were blind to the grouping. Tactile sensitivity was evaluated with a writing brush, which was applied gently in each of the five regions. The patient was told to give a signal if he or she felt any sensation as a result of the brush. Pain sensitivity was evaluated by touching the five regions, using a standardized pin or a blunt instrument. The patient was told to describe the nature of the stimuli as sharp or blunt. The patients were requested to close their eyes during the tests. Each test was repeated four times and the stimuli were scored from 0 to 4, where 0 represented no correct response among the four stimuli and 4 represented all correct responses. At each time point (preoperative, 1 week, 1 month, 3 months, 6 months and 1 year after surgery), in each of the five regions, and in each type of test (tactile sensitivity and pain sensitivity), a relative value was determined for every patient as follows:

<SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='relative value=score of the affected sidescore of contralateral side’>relative value=score of the affected sidescore of contralateral siderelative value=score of the affected sidescore of contralateral side
relative value = score of the affected side score of contralateral side

This method proved feasible as no record of 0 appeared in the contralateral side. The qualitative tests at the 1-year postoperative evaluation were assessed based on the following definitions: normal score ≥3; abnormal score <3.

Student’s t test was used for the continuous variables, and the χ 2 test was used for the categorical variables. A SAS 6.04 statistical software package was used. P < 0.05 was considered to be significantly different.

Results

Three cases were excluded from the study. The reason in two cases was postoperative diagnosis of malignant tumour (one malignant pleomorphic adenoma, in group A; one papillary adenocarcinoma, in group B). These two patients underwent radiotherapy postoperatively. The third patient was diagnosed with bilateral Warthin’s tumour following a CT scan and histological examination. This patient, undergoing bilateral parotidectomy, was excluded for inability to compare the sensory function bilaterally.

Eighty-three of ninety patients with benign tumour were followed-up (45 males; 38 females). Their ages ranged from 19 to 78 years with a mean age of 52.9 years. Group A had a mean age of 53.6 years (range 19–74 years); group B had a mean age of 53.7 years (range 24–75 years); group C had a mean age of 51.4 years (range 27–78 years). Of 83 patients, 17 (four in group A, six in group B, seven in group C) underwent total parotidectomy. The others underwent superficial parotidectomy. In all 83 cases, the facial nerve and its branches were preserved carefully. The mean diameter of the lesions was 2.5 cm (range 0.7–4.2 cm). The postoperative histological diagnoses of the 83 patients varied: 43 pleomorphic adenoma, 29 Warthin’s tumour, 5 basal cell adenoma, 2 myoepithelioma, 1 hemangioma, 2 lymphoepithelial lesions and 1 neurilemmoma. No recurrence occurred postoperatively.

The main trunk of GAN separated directly into three branches in 19 patients (23%; 6 of 28 in group A, 5 of 27 in group B, 8 of 28 in group C, no significant difference between the three groups). In the remaining 64 patients (77%), the lobular branch had a common trunk with the posterior branch.

The mean operating time was 115.3 min for group A (SD = 26.1 min), 122.5 min for group B (SD = 31.5 min) and 123.6 min for group C (SD = 37.3 min). There was no significant difference in operating time between the three groups (Student’s t test , P > 0.05).

The preoperative results for tactile and pain sensitivity in each group were similarly good. In all patients, tactile and pain sensitivity decreased 1 week after surgery. This occurred in all regions, but mainly in the lobular and infra-auricular regions. Sensory improvement occurred at different rates, as demonstrated by different slopes of the curves. Sensory recoveries evaluated with the two sensation methods were similar, but the recovery of pain sensitivity seemed to be rapid compared with tactile sensitivity ( Figs 1 and 2 ).

Fig. 1
Changes in evaluation of tactile sensitivity during the 1-year period after parotidectomy.

Fig. 2
Changes in evaluation of pain sensitivity during the 1-year period after parotidectomy.

In the superior helix and the pre-auricular region, sensory deficit was not significant and patients reported negligent sensory deficit 1 year postoperatively. In the posterior-auricular region, the decline in sensitivity occurred 1 week or 1 month postoperatively when the posterior branch was sacrificed (groups A and C). Sensory function recovered at the subsequent postoperative evaluation. In the posterior-auricular region, sensory function reached the preoperative level 6 months postoperatively in all three groups.

In the lobular region, group C demonstrated a higher score than the other two groups, and the slopes of the recovery curves in groups A and B were similar. At the 1-month postoperative evaluation, the sensitivity of the lobular region improved in all groups, but was best in group C. Six months after surgery, the results in group C reached the preoperative level. In groups A and B there were still sensitivity deficits, they improved very slowly and remained the same at the 1-year postoperative evaluation.

In the infra-auricular region, sensation recovered more quickly in group C, followed by group B and group A. As shown in Figs 1 and 2 , the difference between the three groups tended to minimize at 6 months postoperatively. Until 1 year after surgery, the results in the three groups were close to the preoperative levels.

The results of the qualitative tests at the 1-year postoperative evaluation are summarized in Table 1 . Recovery of tactile sensitivity in the lobular region was 96% in group C, 57% in group A and 63% in group B. Recovery of pain sensitivity in the lobular region was 100% in group C, 21% in group A and 41% in group B. There were significant differences between group C and the other groups in the lobular region, both in tactile sensitivity and pain sensitivity. At the 1-year postoperative evaluation, there was no significant difference in sensory deficits evaluated with the two sensation methods between the three groups in the remaining four regions.

Feb 8, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on The feasibility and significance of preservation of the lobular branch of the great auricular nerve in parotidectomy
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